Although I love the GW skill system, this can lead to some very overpowered builds. Even now, a few years after the release of the original Guild Wars, they have to do regular updates to keep people from using this 'Invincibility-builds'(first thing that pops to mind is the 55-build, which still works atm, but isn't really effective anymore 'cause of the AI update)
So thumbs up for skill synergy, but same story as always: it should be balanced.